John C. Semple    WAT                          

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 Eurybia Nees 

EURYBIAN ASTERS

Eurybia Nees is an predominantly eastern North American x=9 genus of some 28 species of white and blue-purple rayed asters with flat-topped arrangement of heads (except in some species of subg. Heleastrum), phyllaries usually with thumbnail-shaped dark chlorophyllous zone and large marginal hairs.  Some species of subg. Eurybia are native to western North America. 

Eurybia includes two subgenera and nine sections following Nesom's 1994 treatment. Xiang and Semple (1996) found that species representing the two subgenera were closely related in a clade that included a cultivar of Aster amellus, which is enigmatic since the two genera are not closely related within the tribe.  Sericocarpus was found to be the sister group to the Eurybia clade by Xiang and Semple (1996; treated as Aster), but this is likely an artifact of the data set.  Brouillet, Allen, Semple and Ito (2001) found some support for Nesom's treatment, although additional work was needed to resolve the relationships of the several species groups that formed a polytomy at the base of the Eurybia-Machaerantherinae clade.  The Herrickia group formed one of these polytomies, but other groupings proposed by Nesom and listed below were not supported. Brouillet, L., L. Urbatsch & R.P. Roberts (2004) presented DNA sequence data supporting recognition of Oreostemma, Herrickia, Eurybia and Triniteurybia (a new monotypic genus) the formed a grade at the base into the Machaerantherinae.

Summary of infrageneric classification

All species of Eurybia have been treated as members of Aster in North American floras.  The nomenclature below is a significant shift in what had been standard, but it is strongly supported on the basis of morphology because the species are not genetically related to members of the Eurasian genus Aster.  Members of sect. Eurybia (Biotia) have heart-shaped basal leaves, while those of other sections have oblanceolate or obovate basal leaves.  Nesom divided subg. Eurybia into five sections, while I have lumped sect. Radulini into sect. Calliastrum here.   

Eurybia subg. Eurybia

Eurybia sect. Eurybia Eurybia sect. Eurybia (Biotia)

• Eurybia chasei
• Eurybia chlorolepis; habit, North Carolina
• Eurybia divaricata; habit, North Carolina
• Eurybia furcata
• Eurybia jonesiae; habit, heads, involucre, Georgia
• Eurybia macrophylla; habit, Ontario
• Eurybia schreberi; habit, cultivated Ontario, head